I've noticed many lots going negative on LC-C report.  Trying to reproduce the problem I see where it is very easy to send the  Lot negative.  If the material consumed is coming out of more than one lot, the first lot number remains in the data field on the screen after that lot is reduced.  If you accidentally hit return without entering a different lot, the same lot number will be used sending the lot negative.  I don't remember having this problem when I first started using LC for a few items.  Is this dealt with in a default setting some place?  Seems like it used to complain if the lot was 0 and you tried to use it.